Births = Deaths
A dynamic balance between births and deaths.
Population Growth Curves
Reproductive strategies: Many offspring with low parental care
Example fish J-shaped growth curve
Few offspring with high parental care Example mammals S-shaped growth curve
Population Growth Curves
Environmental resistance: combination of biotic and abiotic factors that may limit population increase Predators, competitors, disease Adverse weather, limited food/nutrients
Biotic Potential and Environmental Resistance
Density Dependence and Critical Numbers
Factors of environmental resistance are either: density-independent: effect does not vary with
population density; e.g., adverse weather density-dependent: effect varies with
population density; e.g., infectious disease Critical number: the lowest population
level for survival and recovery
Mechanisms of Population Equilibrium
Predator–prey dynamics Competition
Predator–Prey Balance: Wolves and Moose
Absence of natural enemies allows a herbivore population to exceed carrying capacity, which results in overgrazing of the habitat.
The herbivore population subsequently crashes.
The size of the herbivore population is maintained so that overgrazing or other overuse does not occur.
A single species that maintains biotic structure of the ecosystem
Example: Pisaster ochraceus: a starfish
that feeds on mussels (Mytilus californianus) , keeping them from blanketing the rocks
Pacific coast intertidal zone
Territoriality: defense of a resource against individuals of the same species Results in priority access and use of resources
How do wolves and songbirds establish territory?
Grasslands contain plants with both fibrous roots and taproots
Coexist by accessing resources from different soil levels
Introduced Species Examples (Long Island):
Mute swans Starling House Sparrows Gypsy Moths Japanese Beetles Pheasants Phragmites Eurasian fresh water clam And LOTS MORE!!!
European Green Crab – Native Species
Asian Shore Crab – Introduced Competitor Introduced to New
Jersey in 1988 Spread up to Maine Native Species are
European Green Crab
Asian Shore Crab
Mechanisms of Species Adaptation Change through natural selection
Selective pressure determines which organisms survive and reproduce and which are eliminated.
Adaptations to the Environment
The Limits of Change
Adapt Move (migrate) Die (extinction)
Vulnerability of different organisms to environmental changes
Prerequisites for Speciation
Original population must separate into smaller populations that do not interbreed with one another. List some ways this might happen.
Separated populations must be exposed to different selective pressures. Example: arctic and gray fox
Speciation: Galápagos Finches
Ecosystem Responses to Disturbance
Ecological succession Disturbance and resilience Evolving ecosystems